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package com.ui4j.bytebuddy.instrumentation;

import com.ui4j.bytebuddy.instrumentation.method.MethodDescription;
import com.ui4j.bytebuddy.instrumentation.method.bytecode.ByteCodeAppender;
import com.ui4j.bytebuddy.instrumentation.method.bytecode.stack.StackManipulation;
import com.ui4j.bytebuddy.instrumentation.method.bytecode.stack.constant.DefaultValue;
import com.ui4j.bytebuddy.instrumentation.method.bytecode.stack.member.MethodReturn;
import com.ui4j.bytebuddy.instrumentation.type.InstrumentedType;
import com.ui4j.bytebuddy.jar.asm.MethodVisitor;

/**
 * This instrumentation creates a method stub which does nothing but returning the default value of the return
 * type of the method. These default values are:
 * 
 * The value {@code 0} for all numeric type.
 * The null character for the {@code char} type.
 * {@code false} for the {@code boolean} type.
 * Nothing for {@code void} types.
 * A {@code null} reference for any reference types. Note that this includes primitive wrapper types.
 * 
 */
public enum StubMethod implements Instrumentation, ByteCodeAppender {

    /**
     * The singleton instance.
     */
    INSTANCE;

    @Override
    public InstrumentedType prepare(InstrumentedType instrumentedType) {
        return instrumentedType;
    }

    @Override
    public ByteCodeAppender appender(Target instrumentationTarget) {
        return this;
    }

    @Override
    public boolean appendsCode() {
        return true;
    }

    @Override
    public Size apply(MethodVisitor methodVisitor,
                      Context instrumentationContext,
                      MethodDescription instrumentedMethod) {
        StackManipulation.Size stackSize = new StackManipulation.Compound(
                DefaultValue.of(instrumentedMethod.getReturnType()),
                MethodReturn.returning(instrumentedMethod.getReturnType())
        ).apply(methodVisitor, instrumentationContext);
        return new Size(stackSize.getMaximalSize(), instrumentedMethod.getStackSize());
    }
}